The field of the invention is catheters, and in particular catheters inserted into the central venous system.
Oxygen is essential to human life. An immediate cascade of pathologic processes is triggered in response to a decrease in oxygen delivery. Since oxygen is not stored in sufficient quantities in the body, inadequate oxygen transport to the cells for even very brief periods of time can result in organ failure and death. Thus our ability to monitor and increase oxygen delivery to the body is essential to preventing and reversing organ dysfunction (such as heart, kidney and liver failure or coma) and death. The goal is to balance oxygen supply with tissue oxygen demand.
In an effort to properly balance oxygen supply and demand a number of measurements are commonly made. Current monitoring techniques include continuous electrocardiographic monitoring, measurement of blood pressure, measurement of skin temperature and capillary refill. These noninvasive techniques provide little information regarding hemodynamic status and/or oxygen delivery to the brain or body (tissue).
Mixed venous oxygen saturation (SvO2) is the amount of oxygen in blood taken from a vessel coming from the right side of the heart going into the lungs. This reflects the amount of oxygen being delivered to the tissues. When oxygen delivery to the tissues is inadequate, the SvO2 is low. When oxygen delivery to the tissues is adequate, the SvO2 is normal or high. This is the physiological basis for using SvO2 as the earliest indicator of response to therapy during patient treatment.
Ideally, SvO2 is drawn from a pulmonary artery catheter which is approximately 100 centimeters long and is placed into a vein that accesses the right side of the heart and then into the pulmonary artery. However, placement of a pulmonary artery catheter is extremely difficult and can be impractical during cardiac arrest and severe shock due to low blood pressure and may actually increase patient mortality.
The central venous system avoids traversing the heart and can be more easily accessed. Thus, a number of studies have supported the substitution of central venous (right atrial or superior vena cava) oxygen saturation (ScvO2) for pulmonary artery blood oxygen saturation (SvO2). The central venous blood can be obtained much more easily than blood from the pulmonary artery because the heart does not need to be traversed.
Central venous measurement of oxygen saturation (SvO2) is currently achieved by puncture of the central venous circulation (CVC) system (i.e., internal jugular vein, subclavian vein or femoral vein) and insertion of an intravascular catheter device such as that disclosed in U.S. Pat. No. 5,673,694. Such CVC catheters employ fiber optics to measure SvO2 as described, for example, in U.S. Pat. Nos. 5,754,716 and 4,711,522. They are relatively short (i.e., less than 30 cm in length) and inflexible devices which can remain in place for only a short time (e.g., generally less than 7 days).
The use of CVC catheters to measure oxygen saturation and blood pressure from the superior vena cava or right atrium has a number of drawbacks. These CVC catheter insertions are known to be associated with complications of lung puncture (pneumothorax), major hemorrhage, neck hematoma, carotid artery puncture, cardiac dysrhythmias and infection. In addition, because they can remain in place for only a short time, repeated insertions are necessary when monitoring is required over a long time period.
Peripherally inserted central venous catheters have been available for many years to administer fluids such as parenteral nutrition, chemotherapy, vasopressor (adrenalin like medications), antibiotics and other hypertonic/caustic solutions. These catheters are also used for blood draws. These catheters are inserted into peripheral veins (generally the antecubital, basilic or cephalic veins) and advanced into the central (deep) venous system with the tip ideally positioned in the superior vena cava or right atrium thus allowing for dilution of infused fluids.
The use of such peripheral catheters avoids the complications associated with the direct puncture of the central venous circulation system and they can remain in place for extended periods of time. However, due to their longer length, smaller diameter and greater flexibility, peripheral catheters have not been used for rapid infusion measurement of central venous blood pressure or continuous central venous oximetry.